The major goal of this proposal is to understand mechanisms that underlie the genesis of invasive colon and breast carcinoma by studying the epithelial to mesenchymal transition (EMT). The defining event for EMT is disruption of E-cadherin-mediated cell-cell adhesion, which results in loss of epithelial morphology and acquisition of a motile, mesenchymal phenotype. The cytoplasmic tail of E-cadherin is bound to beta-catenin and p120 catenin (p120ctn). Although the contribution of free beta-catenin to tumor progression has been studied extensively, the functions of p120ctn have not been elucidated in detail in this regard. This proposal is based on the hypothesis that p120ctn functions independently of E-cadherin in the cytoplasm and nucleus as a consequence of EMT and that these functions are linked to the behavior of invasive carcinoma cells. Four specific aims are proposed to address this hypothesis. Aim 1 will determine the expression and sub-cellular localization of p120ctn during the EMT using confocal laser microscopy and 3-D reconstruction. In addition, the prognostic significance of p120ctn expression and localization will be assessed by automated analysis of tissue microarrays of colon and breast cancers. Aim 2 will use RNAi to establish the contribution of p120ctn to the migration dynamics of invasive carcinoma cells and progression in vivo using established orthotopic models. In Aim 3, the hypothesis that p120ctn influences the activation of specific Rho GTPases that are necessary for the EMT and migration of invasive carcinoma cells will be evaluated. The emphasis of these studies will be on the Rho A and Rho C isoforms. The final aim will address the role of p120ctn in the important problem of cadherin switching in carcinoma. Loss of E-cadherin during EMT is correlated with up-regulation of N-cadherin, which has been implicated in migration and invasion, p120ctn associates with the transcriptional repressor Kaiso during the EMT and Kaiso consensus-binding sites exist in the N-cadherin promoter. Thus, the hypothesis will be examined that during the EMT a population of p120ctn translocates into the nucleus where it interacts with Kaiso and inhibits its ability to repress the expression of N-cadherin. In addition to its postulated role in cadherin switching, p120ctn binds to the JMD of N-cadherin but the potential importance of this interaction for the tumor promoting functions of N-cadherin has not been studied. Aim 4 will undertake a rigorous analysis of N-cadherin regulation by p120ctn.